1. Technical Field
Embodiments of the invention relate to a wafer aligning apparatus. In particular, embodiments of the invention relate to a wafer aligning apparatus adapted to load a wafer into a process chamber such that the center of the wafer is aligned and a related method.
2. Description of Related Art
In general, semiconductor devices are fabricated by sequentially performing a series of unit processes, such as photolithography, vapor deposition, etching, diffusion, metal wiring, and ion implantation. A unit process apparatus is adapted to perform a unit process on wafers comprises a process chamber that performs the unit process of that unit process apparatus on a wafer, and a load lock chamber that temporarily stores the wafer before it is loaded into the process chamber and after it is unloaded from the process chamber. The unit process apparatus also comprises a transfer chamber connected to both the process chamber and the load lock chamber, and the transfer chamber comprises a wafer transfer robot that transfers the wafer between the process chamber and the load lock chamber.
Further, wafers are supplied to the load lock chamber in units of lots comprising about twenty five or twenty six wafers stacked in a cassette. In addition, the wafers are supplied from the load lock chamber to the process chamber one at a time.
Additionally, each unit process apparatus comprises an aligning chamber that aligns a wafer one final time before the wafer is loaded into a process chamber. The wafer alignment required to perform each unit process comprises not only the alignment performed in the aligning chamber, but also flat zone alignment, which is performed on wafers in units of cassettes before the cassettes are supplied to the load lock chamber.
However, even if flat zone alignment is performed on the wafers in a cassette before those wafers are provided to a unit process apparatus, the cassette in which the wafers are stacked is manually placed in a load lock chamber of the unit process apparatus by an engineer or a skilled person. Thus, the wafers stacked in the cassette may be moved minutely and misaligned when the cassette is moved or when it is placed in a load lock chamber. Thus, flat zone alignment is performed on wafers in units of cassettes before the wafers are provided to a unit process apparatus, and, in each unit process apparatus, each wafer passes through an aligning chamber before it is provided to a process chamber so that the wafer will be provided to the process chamber precisely aligned.
However, a relatively small amount of time is spent performing a unit process on a wafer in a unit process apparatus, while a relatively large amount of time is spent supplying the wafer to a process chamber. This difference is a principal factor that reduces the productivity of a unit process apparatus.
In particular, in a unit process apparatus, each wafer that is transferred from a load lock chamber to a process chamber must pass through an aligning chamber before it is provided to the process chamber, which increases wafer transfer time and thereby reduces the productivity of the unit process apparatus.